I searched and downloaded a Linux distribution and a multi-season Linux documentary series, and I’ve noticed that Fopnu keeps re-hashing those files. This seems odd because the files were already hashed and present in Fopnu.

This repeated hashing is putting unnecessary load on my PC.

Secondly, why is Fopnu hashing the files again at all?

If the files are already present and have been hashed—and since identical files should share the same universal hash. What is the need for Fopnu to start hashing them again?

Are you downloading with a program other than fopnu and sharing that folder in fopnu? If so, you really shouldn't share folders that other programs are downloading to. That folder, the file within, are going to keep hashing, the file keeps changing / being updated.
Please explain more about where you are seeing all this hashing, what folders, etc...

i searched inside fopnu and downloaded from inside fopnu, that was odd and main reason to raise this request

Are you sure no other program was downloading into that folder? On Linux for me I have my fopnu downloads folder in my library, not shared with the public, but in there. When I download something in fopnu it shows up in my downloads folder in my library and the status updates how complete the file is as it's downloading, and then hashes at the end to be sure its complete. What do you see in your downloads folder, especially when you are downloading? Is it the downloading file that keeps hashing? Does it keep hashing the complete file?